I wonder why they didn't include the machine itself in that chart?
It's an interesting subject Sierra. One that I too have been pondering because it's part of taking better care of my budget, my equipment and myself.
I'm in much the same situation as yourself in that I have to pay for everything (except the machine) and at the moment I've switched to a machine I have paid for because the original Resmed 9 became too dangerous to use.
As well as considerations of cost I am conservative by nature so I agree that the lowest frequency generally makes the most sense.
However I think there would need to be scope for higher frequency in some circumstances because, as you have experienced, not all headgear is designed to function properly and some deteriorate more rapidly than others especially if you wash it too frequently. (which I did with my first one)
My first Philips Nuance nasal pillows mask lasted 2.5 years held together with staples and tape.
The second Philips Nuance lasted 1.5 years held together with twist ties.
I just switched to my third Philips Nuance and it makes a stupendous difference although it's exactly the same mask.
It seats and seals far more easily and leaks a lot less during the night and it feels more comfortable and more secure.
Yet I still consider the old mask to be functional, I used the first one for far longer, so what was wrong with the second one?
A bunch of little things. The elastic in the headgear has become a bit slack and the velcro isn't quite as sharp anymore and the cushions are not as bouncy as they used to be.
Each of those things on their own is relatively minor and, as you have implied, can be rectified with a little improvisation, but the overall effect was turning into a nightmare.
So yes annual replacement of most items would be a wonderful upgrade for me as long as there was scope for earlier replacement of badly designed gear.